Water gas shift (WGS) reactors for the catalyst-driven conversion of CO and water to H2 and CO2 are widely known in the chemical and petroleum industries. The reactors are also useful in processes relating to the conversion of fuels, including gasoline, diesel, methanol, ethanol, natural gas, and coal, to H2 for use in generation of electricity by fuel cells for use in, e.g., fuel cell vehicles, mobile power, home electricity, and stationary power applications.
The reversibility of the WGS reaction at equilibrium ordinarily results in an inefficient reaction necessitating a bulky reactor and producing a H2 product contaminated with a high concentration of unconverted CO, and with an undesirable concentration of CO2. Carbon monoxide contamination in the hydrogen fuel produced from a conventional WGS reactor has detrimental effects on fuel cell performance, including poisoning the platinum-based catalyst at the anode of the fuel cell. For example, 30 ppm of CO may cause a 48% drop in the output cell voltage of a proton exchange membrane (PEM) fuel cell, from 0.6 volts to 0.31 volts at 150 amperes. Output decreases of up to 90% at a current density of 650 amperes/ft2 may be expected from the use of an H2 product containing 100 ppm of CO. Additionally, CO2 in excess quantities dilutes the H2 product and increases the mass transfer resistance as well as producing CO via the reverse WGS reaction at the anode, thereby further reducing fuel cell efficiency.
Accordingly, there is need in the art for novel WGS reactors comprising membranes which are able to shift the equilibrium of the reaction to production of H2 while minimizing CO contamination, thereby enhancing the purity of the final product. There is further need in the art for reactors which are capable of efficiently producing hydrogen via the WGS reaction, while requiring a smaller reactor size, thereby enhancing their utility in applications where space is at a premium such as in fuel cells for use in electric or hybrid vehicles.